<PAGE>

                                                                   Exhibit 10.11

                           David Nichols Realty, Inc.

71 East Pennington         Tucson, Arizona 85701                 520-624-0426





                           COMMERCIAL LEASE AGREEMENT



                                    Between

                             Larry Michael Sandusky
                                       &
                             Rebecca Anne Sandusky
                                            Landlord
--------------------------------------------------------------------------------


                                      and


                        Chorum Technologies Inc., Tenant


--------------------------------------------------------------------------------

                                     Dated

                                June 8th, 2000
<PAGE>

                          COMMERCIAL LEASE AGREEMENT

                                     INDEX

<TABLE>
<S>  <C>                                                          <C>
 1.  LEASED PREMISES                                              1

 2.  USE OF LEASED PREMISES                                       1

 3.  ZONING                                                       1

 4.  COMPLIANCE WITH LAWS                                         1

 5.  CONDUCT OF BUSINESS                                          1

 6.  TERM                                                         2

 7.  RENT                                                         2

 8.  MONTHLY RENTAL PAYMENTS                                      2

 9.  SECURITY DEPOSIT                                             2

10.  WHERE PAYABLE                                                3

11.  MAINTENANCE OF LEASED PREMISES                               3

12.  UTILITIES AND GLASS                                          3

13.  ADVANCE POSSESSION                                           3

14.  ALTERATIONS AND ADDITIONS                                    3

15.  LIENS CREATED BY TENANT                                      4

16.  LEAKING ROOF                                                 4

17.  DAMAGE OR INJURY TO PERSONS OR PERSONA L PROPERTY            4

18.  LANDLORD RULES                                               4

19.  LIABILITY INSURANCE                                          4

20.  LANDLORD'S EXEMPTION FROM LIABILITY                          5

21.  LANDLORD'S CASUALTY INSURANCE                                6

22.  INSPECTIONS                                                  6

23.  FIRE OR EQRTHQUAKE                                           6

24.  LIGHTING AND OTHER FIXTURES                                  6

25.  BANKRUPTCY                                                   6

26.  WAIVER BY LANDLORD                                           7

27.  LEASE TRANSFER                                               7

28.  REASONABLE CONSENT                                           8

29.  TENANT CONTINUING RESPONSIBILITY                             8

30.  ENFORCEMENT OF LEASE                                         8

31.  CHANGE IN LEASE                                              8
</TABLE>
<PAGE>

<TABLE>
<S>  <C>                                                          <C>
32.  CONTINUING LEASE AFTER EXPIRATION                            8

33.  SUIT TO ENFORCE TERMS OF LEASE                               8

34.  POSSESSION AT EXPIRATION OF THIS LEASE                       9

35.  IF LANDLORD CANNOT DELIVER POSSESSION OF LEASED PREMISES     9

36.  INDEPENDENT COVENANT FOR PAYMENT OF RENT                     9

37.  IF LEASED PREMISES ARE DESERTED BY TENANT                    9

38.  LANDLORD'S RIGHT TO PLACE "FOR SALE" OR "FOR LEASE" SIGN     9

39.  RETROACTIVE RENT CLAUSE                                      9

40.  BROKERAGE FEE                                                9

41.  SUBMISSION OF LEASE                                         10

42.  GENDER                                                      10

43.  SIDE HEADINGS                                               10

44.  MORTGAGE                                                    10

45.  SIGNS                                                       10

46.  KEEPING LEASED PREMISES CLEAN                               11

47.  NON-PAYMENT OF RENT                                         11

48.  LANDLORD'S DAMAGES                                          11

49.  EQUIPMENT, ROOF, WALLS AND OTHER REPAIRS                    11

50.  FINANCIAL STATEMENT                                         12

51.  DISCLAIMERS                                                 12

52.  TIME OF ESSENCE                                             12

53.  BINDING ON HEIRS, ETC.                                      12

54.  TENANT IMPROVEMENTS                                         12

55.  LANDLORD'S LIEN                                             12

56.  AMERICANS WITH DISABILITIES ACT                             12

57.  CONDITION OF LEASED PREMISES                                12

58.  HAZARDOUS WASTE                                             13

59.  CONDEMNATION                                                13

60.  NOTICES                                                     14

61.  LANDLORD'S DEFAULT                                          14

62.  WARRANTY OF AUTHORITY                                       14

63.  FORCE MAJEURE                                               14
</TABLE>

<PAGE>

COMMERCIAL LEASE AGREEMENT

     THIS LEASE, made this 8th day of June 2000 between Larry Michael Sandusky &
Rebecca Anne Sandusky (hereinafter called "LANDLORD"), AND Chorum Technologies,
Inc., (hereinafter called "TENANT"), and David Nichols Realty, Inc (hereinafter
called "PROCURING BROKER" or "AGENT").

     1.  LEASED PREMISES: Landlord hereby leases to Tenant and Tenant leases
from Landlord for the term, at the rental, and upon all the conditions set forth
herein, that certain real property situated in the County of Pima, State of
Arizona, commonly known as:

            221 E. 6th Street, in the County of Pima, City of Tucson, State of
Arizona

and described on Exhibit A attached, Leased Premises outlined in yellow hereto
and made a part hereof. Said real property including the land and all
improvements thereon, is herein called the "Leased Premises."

     2.  USE OF LEASED PREMISES. The Leased Premises shall be used only as:

                        Office and Light Manufacturing

     3.  ZONING. It is agreed that the zoning has been investigated by Tenant
and determined by the Tenant to be correct, in all respects, for the business
use as stated herein.

     4.    COMPLIANCE WITH LAWS. The Tenant agrees to conduct the business in a
legal manner and in accordance with Municipal, County, State and Federal
regulations and requirements, and to Zoning ordinances.


           The Tenant shall faithfully and promptly execute and comply with all
present and future statutes, ordinances, soles, orders, regulations and
requirements of the Federal, State, City and County authorities and o(Pounds)
any and all their departments and bureaus applicable to said Leased Premises
and the use thereof. Should the Tenant, or the Health, building or City, County,
State or Federal authorities require any changes or improvements in or to the
Leased Premises, the Tenant shall first obtain the written consent from the
Landlord for such changes, and all such changes or improvements shall be done at
the sole expense and risk of the Tenant. The Tenant agrees to comply with all
provisions, covenants, conditions and restrictions as recorded in the office of
the County Recorder of Pima County, Arizona. Any interruption or stoppage in the
use and occupancy of the Leased Premises shall not affect the rental terms,
conditions and covenants contained in this Lease.

     5.    CONDUCT OF BUSINESS. Tenant shall not leave the Leased Premises
unoccupied or vacant but shall throughout the term of this Lease conduct and
carry on the type of business for which the Leased Premises are leased at its
usual business hours and manner.
<PAGE>

     6.  TERM. TO HAVE AND HOLD the same to the said Tenant from the 8/th/ day
of June, 2000 through the 8/th/ day of October, 2000.

     7.  RENT. And the said Tenant, in consideration of the leasing of the
premises hereinabove set forth, covenants anal agrees with the Landlord to pay
the said Landlord as! Rent for , the property the total suns of Thirty Two
Thousand Four Hundred Sixty Eight Dollars and Ninety-Six Cents ($32,468.96)
lawful money of the United States of America, which amount is now due and
payable.

     8.  The above rent includes an amount presently equal to Two percent (2%)
of the gross monthly rent (gross monthly rent shall include rent and Tenant's
m6nthly payment of real property tax and insurance reimbursement as described
below), which. amount is for the TWO percent (2 %) "Business Privilege License
Tax" as imposed by the City of Tucson. In the event the City ,or State, or both,
should impose an increase or additional tax, the Tenant agrees to pay said
increase and such additional tax. The Landlord, in turn, shall pay these amounts
to the proper Governmental body. Said tax, as of the date of this Lease, is One
Hundred Fifty Nine Dollars and Sixteen Cents ($159.16) per month. The Tenant
hereby agreed to pay any and all other taxes levied or assessed by State,
County, and/or City or Federal authorities applying to or affecting the Leased
Premises, including all taxes on all merchandise and stock and all taxes on all
equipment as owned by Tenant or on Landlord's equipment used by Tenant, and to
pay all license, fees, sales taxes for conducting the business.

     Tenant agrees to pay as part of the above rent amount any real property
taxes levied for the 2000 tax year, prorated as of 2000. Tenant shall pay his
share of the annual real property tax only for the term of the lease. It shall
be computed on a prorated share of square footage per unit, if there are
multiple units. Tenant's percentage of their space to total property is 47% as
designated by Tax Code # ###-##-####. Taxes for the 2000 Tax Year are $12,500.
The monthly cost is Four Hundred Eighty Nine Dollars and Fifty Eight Cents
($489.58) per month for each month of the lease.

     Tenant agrees not to deduct from the herein rental payments any cost or
expense whatsoever involving repairs, maintenance or alterations to, the Leased
Premises or for anything else, unless written consent is first obtained by the
Tenant from the Landlord or from the Agent.

     9.  SECURITY DEPOSIT. On or before the date of execution of this Lease,
Tenant will deposit with the Landlord the total sum of Eight Thousand One
Hundred Seventeen Dollars and Twenty Four Cents ($8,417.24) (herein after
referred to as "Security Deposit").

     Security Deposit shall be held by the Landlord as Security for the faithful
performance by Tenant of all the terms and conditions of this Lease to be kept
and performed by Tenant during the term hereof. If Tenant defaults with respect
to any provisions of this Lease, including; but not. limited to the provisions
relating to the payment of rent, Landlord may (but shall not be required to)
use, apply or retain all or any part of this Security Deposit for the payment of
any rent or other sums in default, or for the, payment of any amount which
Landlord may spend or become obligated to spend by reason of Tenant's default ,
or to compensate Landlord for any other loss or damage which Landlord may suffer
by reason of Tenant's default. If any portion of said deposit is so used or
applied Tenant shall, within 5 days (5) days after written demand therefor
deposit cash with Landlord in an amount sufficient to restore the Security
Deposit to its original amount and Tenant's failure to do so shall be a default
under this lease. Landlord shall not be required to keep this Security Deposit
separate from its general funds, and Tenant shall not be entitled to interest on
such deposit.  If Tenant shall fully and faithfully perform every provision of
this lease to be performed by it, the Security Depositor any balance thereof
shall be returned to Tenant (or, at Landlord's option, to the last assignee of
tenant's interest hereunder) within ten (10) days following expiration of this
Lease term. In the event of termination of Landlord's interest in this Lease,
Landlord
<PAGE>

shall transfer said Deposit to Landlord's successor in interest and shall have
no further obligation with respect thereto.

     10.  WHERE PAYABLE. All rental payments shall be made payable to the order
of

                               Mr. Mike Sandusky
                              1760 Calle Del Voso
                            Tucson, Arizona  85737
          During the entire term of this Lease, unless otherwise designated by
Landlord.


     11.  MAINTENANCE OF LEASED PREMISES. Tenant at all tunes during the term of
Lease, at its own cost and expense, shall keep and maintain or cause to be kept
and maintained in good condition and repair, ordinary wear and tear excepted,
walls, flooring, light fixtures and ceiling tiles, and shall use all reasonable
caution to prevent waste, damage or injury.

     12.  UTILITIES AND GLASS. Tenant further agrees to connect to and pay for
all water, fuel, light, power, gas, telephone, and all other utilities used in
or about the Leased premises and the Landlord shall in no way be responsible
therefor. The Tenant hereby agrees to take full responsibility for all plate
glass and other glass in and about the Leased Premises, and should Landlord
require that plate, glass insurance be carried, the premium shall be paid by the
Tenant.

Tenant shall not overload the electrical systems and shall install, after
obtaining Landlord's prior written approval, any additional wiring required for
Tenant's equipment.

     13.  ADVANCE POSSESSION. All terms of this Lease shall be in force from the
initial date of possession of key or by physical occupancy of Leased Premises by
Tenant. Rent shall continue upon expiration of Lease and until key and
possession of Leased Premises is returned to Landlord.

     14.  ALTERATIONS AND ADDITIONS. Tenant shall not make or allow to be made
any alterations, additions or improvements to or on the Leased Premises or any
part thereof without the written consent of Landlord first had and obtained, and
any alterations, additions or improvements to or of said Leased Premises,
including, but not limited to wall covering, paneling and built-in cabinet work,
but excepting movable furniture and trade fixtures installed by Tenant, shall at
once become a part of the realty as further evidenced by the signing and filing
of a UCC-1 designating the Landlord the Secured Party and shall be surrendered
with the Leased Premises if here is a default in complying with the terms of the
lease. In the event Landlord consents to the making of any alterations,
additions or. improvements to the Leased Premises by Tenant, the same shall be
made by Tenant in a good, workmanlike and diligent manner at Tenant's sole cost
and expense, in accordance with law, with Tenant to obtain all applicable
permits. Upon the expiration or sooner termination of the terns hereof, Tenant
shall, upon written demand by Landlord, given at least thirty (30) days prior to
the end of the term, at Tenant's sole cost and expense, forthwith and with all
due diligence, remove any alterations, additions, or improvements made by
Tenant, designated by Landlord to be removed, and Tenant shall forthwith and
will all due diligence, at its sole cost and expense, repair any damage to the
Leased premises caused by such removal.

     15.  LIENS CREATED BY TENANT. The Tenant shall have no power to do any act
or to make any contract that may create or be the foundation for any lien upon
the Leased Premises or other estate of the Landlord in the Leased premises or
upon any building or improvement thereon, and should any such lien be filed; the
Tenant at his own cost and expense shall bond or otherwise charge the same
<PAGE>

within ten (10) days after the filing thereof. If Tenant fails to do so,
Landlord may (but shall not be obligated to) pay such claim and the amount so
paid together with any costs.

     16.  LEAKING ROOF. The Landlord shall not be responsible for any damage
sustained by the Tenant by reason of water leaking through the roof of said
building.

     17.  DAMAGE OR INJURY TO PERSONS OR PERSONAL PROPERTY. The Tenant hereby
agrees to indemnify, defend and save harmless the Landlord from any and all
liability for any damage or injury to person or property caused by or resulting
from the Tenant's failure to perform any maintenance or repair, as required by
the terms and provisions of this Commercial Lease. The Tenant further agrees to
indemnify, defend and save harmless the Landlord from any and all loss, damage
or liability by reason of any injury or injuries to any person, persons or
personal property occurring by reason of Tenant's use or occupancy or through
the fault or negligence of the Tenant, his employees or patrons. Landlord shall
not be responsible for loss or damage to Tenant or his or anyone else's personal
property on the leased premises, for any reason whatsoever, including but not
limited to, fire, flood, weather, maintenance and structural failure of said
Leased Premises. Tenant is to obtain insurance for his leasehold improvements
and personal property and general liability. If Tenant fails to remove such
personal property prior to expiration of the Term it shall become the property
of the Landlord.

     18.  LANDLORD RULES.  The Landlord reserves the right to make such other
and further reasonable rules and regulations as in its judgment may from time to
time be needful and desirable for the safety, security, care and cleanliness of
the Leased Premises and preservation of good order therein. Said rules must be
presented to Tenant in writing, prior to taking effect.

     19.  LIABILITY INSURANCE. Tenant shall, at Tenant's expense, obtain,
maintain and keep in force, by advance payment of premiums, during the term of
this Lease a policy of comprehensive public liability said property damage
insurance insuring Landlord and Tenant against any liability arising out of the
ownership, use, occupancy or maintenance of the Leased Premises and all areas
appurtenant thereto. Such insurance shall be in the amount of not less than
$1,000,000.00 for injury or death of one person in any one accident or
occurrence and in the amount of not less than $1,000,000.00 for bodily injury or
death for more than one person in any one accident or occurrence. Such insurance
shall further insure Landlord and Tenant against liability for property damage
of at least $250,000.00. Alternatively, limits shall be not less than
$1,000,000.00 bodily injury and property damage liability insurance combined
single limit. The limit of any such insurance shall not, however, limit the
liability of the Tenant hereunder. If the Tenant shall fail to procure and
maintain said insurance the Landlord may procure the same, and Tenant shall be
obligated to reimburse Landlord for the cost thereof, within five days of
receipt of the bill therefore. Insurance required hereunder shall be in
companies rated A+ or better in "Best's Insurance Guide." Tenant shall deliver
to Landlord, prior to right of entry, certificates evidencing the existence and
amounts of such insurance. No policy shall be cancelable or subject to reduction
of coverage or non-renewed without 30 days prior written notice being given to
the Landlord. The insurance provided by Tenant shall specify that it is primary
insurance and any insurance maintained by Landlord shall be in excess and not
contributory with Tenant's insurance. Landlord and Tenant agree that they shall
not be liable to the other and hereby release the other for damage to the Leased
premises and to Tenant's improvements and to loss through business interruption
and to loss to personal property from risks insured against under any insurance
policies carried by the parties and in force at the time of such damage. This
release shall apply only to the extent that such loss is covered by insurance.
Tenant shall also maintain worker's compensation insurance as required by state
law.

     20.  EXEMPTION OF LANDLORD FROM LIABILITY. Tenant agrees Landlord shall not
be liable for injury to Tenant's business or for damage to the goods,
merchandise or other property of and/or
<PAGE>

not liable for injury to the person of Tenant as well as Tenants employees,
agents, invitees, customers, contractors or any other person in or about the
property, including but not limited to a vandal. Such exemption of Landlord from
all liability shall apply whether such damage or injury is caused by or results
from fire, utility related damage, weather related damage such as caused by roof
leak, building or plumbing defect related damage or from any other cause,
including but not limited to, the negligence, and/or any agent of Landlord
including an employee or contractor of Landlord as well as whether any such
damage or injury results from conditions arising upon the property, other
portions of the building of which the property is a part or from other sources
or places and regardless of whether the cause of such damage or injury or the
means of repairing the same is inaccessible to the Tenant.

Further, Tenant agrees to waive any statutory provision, case law or legal
authority which is contrary to and/or nullifies/voids in any way such
member/partner protective provisions in the event of any actual or alleged
breach of the lease by the Landlord, the sole remedy shall be against the assets
of the Landlord and no individual member, partner or other associated entity of
the company shall be liable for any damages arising from any act or omission or
neglect including negligence of the Owner or of any other Tenant as well as any
other Tenant's employees, agents, invitees, customers, contractors or any other
person in or about the property, including but limited to a vandal.

Further, Tenant expressly agrees to indemnify, hold harmless and defend
Landlord, any owner of Landlord, such as any shareholder or L.L.C. member as
well as any employee, contractor or other agent of Landlord from claim or
losses, damages or the like, including costs attorney's fees, arising out of all
enumerated causes including but not limited to Tenant's utilization of the
leased premises. All such continuing agreements duties and promises of Tenant
contained in this exemption of Landlord from liability as well as such
continuing duties, obligations and promises of Tenant contained elsewhere in
this agreement shall survive and continue following the end of the lease term
and/or occupancy of Tenant with such indemnification, hold harmless and defend
provisions to apply to any claim, loss, damage, liability or the like made by
Tenant, invitee of Tenant, employee, contractor or other agent of Tenant or any
other third party, including but not limited to another Tenant and including any
and all claims even if caused by the negligence of the Landlord and any Owners
of Landlord and/or agent of Landlord including an employee or contractor of
Landlord.

     21.  LANDLORD'S CASUALTY INSURANCE. Tenant agrees not to do anything,
including, but not limited to, structural changes, which could jeopardize the
Landlord's insurance coverage, create additional risk, fail to comply with a
law, or regulation, or Landlord's insurance company's requirements or cause an
increase in Landlord's insurance premium.

Tenant, each successive month, shall pay the Landlord, in addition to the rent,
one-twelfth (1/12th) of the Landlord's cost of special form - all ask property
damage, liability and casualty insurance ("Property Casualty Insurance"). It
shall be compiled on a pro rata share of square footage per unit, if there are
multiple units. Tenants percentage of their space to total property is 47%.
Monthly Insurance cost to Tenant is Seventy Dollars and Fifty Cents ($70.50)

     22.  INSPECTIONS. The Landlord or his Agent is hereby granted the right and
privilege to inspect the property both inside and outside at any time during the
term of this Lease, between the hours of 10:00 A.M. and 4:00 P.M. Should any of
the leased property be damaged the Landlord shall have the right to demand that
such damage be repaired immediately and at the sole cost, expense and risk of
the Tenant.

     23.  FIRE OR EARTHQUAKE. If at any time during the Lease, the Leased
Premises shall be destroyed by fire, by the
<PAGE>

elements, by earthquake or any other casualty or be so damaged by fire, by the
elements, by earthquake, or any other casualty that, in the reasonable judgment
of Landlord's contractor, the Leased Premises cannot be repaired, rebuilt or
restored within Thirty (30) working days from the date of such damage, this
Lease may, at the option of either party, be terminated by delivering written
notice of termination not later than Thirty (30) days after the date of the
casualty, and rights hereunder shall cease and terminate and the Tenant shall be
entitled to be reimbursed for all rents paid in advance. The Tenant agrees to
give the Landlord access to the Leased Premises so that the necessary repairs,
rebuilding or restoration may be resumed without delay, subject to availability
of insurance proceeds and the ability to obtain necessary permits. It is further
understood and agreed that during the time or times that the Tenant may be
unable to occupy the Leased Premises for the reason above stated, rental shall
abate proportional to the square footage of the Premises which is unavailable
for occupancy, until said Leased Premises are again in condition to be available
for use by the Tenant.

     24.  LIGHTING AND OTHER FIXTURES. The Tenant agrees to furnish and install
at his own sole cost and risk upon, obtaining Landlord's prior written approval,
any additional lighting fixtures, cooling and heating system, needed for
Tenant's efficient operation(s). All said additions and/or alterations shall
become the property of the Landlord, without charge, at the termination of this
Lease.

     25.  BANKRUPTCY. It is hereby mutually agreed, covenanted and understood
that in the event the Tenant shall file a petition in bankruptcy or be
adjudicated a bankrupt, or make an assignment for the benefit of creditor or
take the benefit of any insolvent act or fail in business, then this Lease
shall, at the option of the Landlord, immediately terminate and in no event
shall this Lease be treated as an asset of the Tenant after the exercise of such
option.

     26.  WAIVER BY LANDLORD. The waiver by the Landlord of any breach or
breaches by the Tenant of any one or more of the covenants, agreements,
conditions, or obligations herein contained or the acceptance of any delinquent
payments shall not bar the Landlord's right to declare a forfeiture or to employ
any other rights or remedies of the Landlord in the event of any subsequent
breach of any such or other covenants, agreements, conditions or obligations.
Any entry and/or reentry by the Landlord, whether had or taken by the terms of
this Lease under what is generally known as summary proceedings, shall not be
deemed to absolve or discharge the Tenant from liability hereunder.

     27.  LEASE TRANSFER. The Tenant hereby agrees not to sell, transfer,
sublease, sublet or assign this Lease, or to lease or sublease the whole or any
portion of said Leased Premises without first obtaining the written consent of
the said Landlord, and any attempted assignment of lease or sublease without
such written consent shall be void. Even though the Landlord may give the
written consent to an assignment, subletting or transferring hereof, it is
agreed that no further assignment, subletting or transferring shall be made by
the Tenant without the express consent in writing by the Landlord. Such consent
cannot be unreasonably withheld. The Landlord reserves the right to assign this
Lease to anyone, and at any turn:, without given notice to the Tenant and
Landlord shall be released from all liability and obligation arising hereunder
after the date of such assignment.

     28.  REASONABLE CONSENT. As set forth in paragraph 27 above, Tenant shall
not sublet or assign the Leased Premises without the Landlord's prior written
consent, which consent shall not be unreasonably withheld In determining whether
to grant consent to the Tenant's sublet or assignment request, the Landlord may
consider any reasonable factor. Landlord and Tenant agree that any one of the
following factors, or any other reasonable factor, will be reasonable grounds
for deciding the Tenant's request:

     a.   financial strength of the proposed subtenant/assignee must be at least
equal to that of the existing Tenant;
<PAGE>

     b.   business reputation of the proposed subtenant/assignee must be in
accordance with generally acceptable commercial standards;

     c.   use of the Leased Premises by the proposed subtenant/assignee must be
identical to the use permitted by this lease;

     d.   percentage rents, if a condition of this Lease, of the proposed
subtenant/assignee, or the prospect of percentage rents, must be at least equal
to that of the existing Tenant;

     e.   managerial and operational skills of the proposed subtenant/assignee
must be the same or exceed those of the existing Tenant;

     f.   use of the Leased Premises by the proposed subtenant/assignee will not
violate or create any potential violation of any laws and;

     g.   use of the Leased Premises will not violate any other agreements
affecting the Leased Premises, the Landlord or other Tenants or require Landlord
to make alterations or improvements to the Premises.

     28.  TENANT CONTINUING RESPONSIBILITY. In the event the Landlord gives
consent to the Assignment of this Lease, the Tenant shall still nevertheless
continue to be fully liable and responsible for the full and faithful
performance of each and all of the terms, covenants and conditions herein
contained on the part of the Tenant herein to be performed and observed, and
provided further, that the Assignee shall likewise be deemed to have assumed the
full and faithful performance of said terms, covenants and conditions contained
within the Lease on the part of the Tenant herein to be performed and shall
deliver to the Landlord herein written assumption agreement assuming such
performance as aforesaid.

     29.  ENFORCEMENT OF LEASE. The said Landlord may, at his option, in
addition to any of the rights given by this indenture, enforce any provisions of
the laws of the State of Arizona, or of the United States of America governing
the relations of Landlord and Tenant, with the same effect as though the right
to enforce such provisions were herein specifically set forth. In the event any
provision in this Lease is held invalid by any court of competent jurisdiction,
the remaining provisions in this Lease shall be deemed severable and shall
remain in full force and effect.

     30.  CHANGE IN LEASE. The making, execution and delivery of this Lease has
not been induced by any representation, statement, warranties or agreements
other than those herein expressed. It is mutually agreed by and between the
parties hereto that this agreement supersedes all other previous and/or other
agreements bearing upon the above Leased Premises, and it is further agreed that
no changes to or in this Lease shall be made without being in writing, signed by
all of the parties hereto.

     31.  CONTINUING LEASE AFTER EXPIRATION. In the event that Tenant should
hold over and continue in the occupancy of the Leased Premises after the
expiration of the initial term of this Lease, or any extension thereof, with the
consent of the Landlord, express or implied, the Tenancy shall be deemed to a
tenancy only from month to month, upon the same terms and conditions as exist
and prevail at the time of the termination of the Lease, and subject to increase
in monthly rental at the option of the Landlord. Partial months shall be charged
as a full-month rent.
<PAGE>

     32.  SUIT TO ENFORCE TERMS OF LEASE. In the event of legal action between
any of the signatories to this Agreement to enforce the terms hereof the
prevailing party shall be entitled to reasonable attorneys' fees and court costs
from the party adjudged against.

     33.  POSSESSION AT EXPIRATION OF THIS LEASE. The Tenant further covenants
and agrees with the Landlord that at the expiration of the term mentioned in
this Lease, peaceable possession of the Leased Premises shall be given to the
Landlord, the Leased Premises to be in as good condition as they now are, or as
when first occupied, the usual wear and tear, inevitable casualties and loss by
fire excepted. Transfer of Possession of Leased Premises is defined as when
Tenant returns all keys to Landlord or his agents after vacating Leased
Premises.

     34.  IF LANDLORD CANNOT DELIVER POSSESSION OF LEASED PREMISES. If Landlord,
for any reason, cannot deliver possession of the Leased Premises to Tenant at
the commencement of said term, this lease shall not be void or voidable, nor
shall Landlord be liable to Tenant for any loss or damage resulting therefrom;
but there shall be proportionate deduction of rent covering the period between
commencement of said term and the time when Landlord can deliver possession.

     35.  INDEPENDENT COVENANT FOR PAYMENT OF RENT. The covenant of the Tenant
to pay rent shall at all times be recognized as an independent covenant under
the terms of this Lease and shall in no way be construed to be dependent upon
any other clause, condition or covenant contained herein.

     36.  IF LEASED PREMISES ARE DESERTED BY TENANT. In the event the Leased
Premises shall be deserted or if the Tenant ceased to conduct business without
paying punctually the rent herein called for, then in addition to all other
rights and remedies of Landlord hereunder, at law and in equity, the Tenant
grants to the Landlord or his agent the right to take over possession of the
Leased Premises as agent for the Tenant and do whatever the Landlord deems best
to protect his interest so that the Landlord may obtain the balance of money due
under this Lease, and without the Landlord waiving or relinquishing any of his
rights mentioned in this Lease.

     37.  LANDLORD'S RIGHT TO PLACE "FOR SALE" OR "FOR LEASE" SIGN. The Tenant
hereby grants upon the Landlord or his Agent the right to place a "For Lease"
sign on or in the Leased Premises at any time the tenant vacates the Leased
Premises, at any time there is evidence that the Tenant has ceased to conduct
business in or on the Leased Premises, or within 60 days of the termination of
this lease. Tenant hereby grants the Landlord or his agent., the right to place
a "For Sale" sign at anytime.

     38.  REPAIRS OR REPLACEMENT IN EVENT OF THEFT OR VANDALISM. Notwithstanding
anything to the contrary herein contained, the Tenant agrees to repair or
replace, without delay and at his own sole cost, expense and risk any and all
portions of the Leased Premises that may be damaged by theft, burglary,
vandalism or by malicious mischief.

     39.  RETROACTIVE RENT CLAUSE. Should landlord fail to notify Tenant of his
intent to revise the rental at such time or times as herein specified, such
rental shall continue to be subject to revision upon notification by Landlord as
provided herein and, when so revised, shall be retroactive to the date such
rental should have become effective, regardless of the number of years involved.

     40.  BROKERAGE FEE. David Nichols Realty, Inc and Weststar Mortgage Corp.
shall be recognized as the sole procuring broker for the Lease, or any option,
renewal, extension, addition, or enlargement thereof, or any sale or Lease of
this property, or any portion thereof, to the lessee, regardless
<PAGE>

of whether the terms of this Lease are modified or if the Lease is canceled and
a new Lease entered into. David Nichols Realty, inc. shall be entitled to 6% of
the gross Lease amount as commission, payable by Owner upon the signing of the
Lease, the signing of any renewal or extension, and/or the signing of any new
Lease with the lessee. David Nichols Realty, inc. shall also be entitled to 6%
of the gross sales amount as commission, payable by Owner upon the closing of
any sale of Leased Premises procured by Agent The minimum leasing commission
payable for any Lease is $500.00. This provision applies to, inures to the
benefit of, and binds all parties hereto, their heirs, legatees, devisees,
administrations, executors, successors, and assigns. If David Nichols Realty,
inc. must file an action against any person or entity to enforce the terms of
this brokerage provision, David Nichols Realty, inc., shall be entitled to
recover reasonable attorneys fees and court costs. The undersigned certify: that
they are the legal Owners of the described property, or are the authorized
agent(s) of the legal Owners.

In the event the Tenant requests and receives an assignment of this Lease, the
Agent or Broker shall be entitled to a brokerage fee for any remaining or any
additional term(s). The brokerage fee shall be paid by the Tenant, subject to
all of the above provisions.

     41.  SUBMISSION OF LEASE. Submission of this Lease for examination does
not constitute a reservation of or option for the Leased Premises. This
instrument becomes effective as a Lease upon execution and payment of Security
Deposit and prepaid rent for the four (4) months by Tenant and lease executed by
Landlord.

     42.  GENDER It is further understood that if more than one join in the
execution hereof or may be of the feminine, masculine or neuter gender, the
pronouns and relative words herein used shall be read and understood as if
written in plural, feminine, masculine or neuter, respectively.

     43.  SIDE HEADINGS. The herein side headings are for convenience only, and
do not define, limit or construe the content, of the various articles in this
Agreement"

     44.  MORTGAGE. The Tenant's rights under this Lease are and shall always
be subordinate to the lien of any existing mortgage or mortgages and to any
mortgage or mortgages which the Landlord may and shall have the right to execute
at any time during the term of the Lease or any renewal or extension thereof;
and the Tenant upon request by the Landlord agrees to execute within fifteen
(15) days of request such instrument or instruments permitting a mortgage or
mortgages to be placed upon the Leased Premises so as to subordinate this Lease
to any mortgage or mortgages.

     45.  SIGNS. The Tenant agrees not to place any permanent signs on the
windows, doors or walls or in any other locations on the Leased Premises without
first obtaining the written consent of the Landlord. The Tenant agrees not to
paint, inscribe or erect any outside signs on walls or roofs without first
obtaining the written consent of the Landlord; and should the Landlord give such
written consent, then all such signs and paint shall be removed by the Tenant at
least thirty days prior to the expiration of this Lease, and the walls, roof,
front and tear yards left in good condition, and free from any holes or damage.
Tenant is aware that there is a sign permit fee that is at Tenant's cost.
Landlord shall not withhold reasonable consent, except that Tenant must install
any City approved sign within the space provided for signs and Tenant shall be
solely responsible for obtaining all necessary approvals.

     46.  KEEPING LEASED PREMISES CLEAN. The Tenant agrees to keep the Leased
Premises inside and outside clean acrid neat at all times, including sidewalks,
windows, parking area and front and rear yards; and to keep sidewalk free of any
obstruction. Tenant shall be solely responsible for prompt removal and proper
disposal of all trash and garbage, and all removal of graffiti.
<PAGE>

     47.  NON-PAYMENT OF RENT. The Tenant further agrees with the Landlord that
upon the non-payment of the whole or any part of the rent or other amounts
payable hereunder at the time when same is above promised to be paid by the said
Tenant and said non-payment of rent continues for a period of ten (10) days,
after written notice from Landlord, or in the event said Leased Premises or part
thereof shall be deserted (which shall mean Tenant's failure to conduct business
in the Premises thirty (30) consecutive days or more without prior notice to
Landlord) during said term or of the breach of any of the other terms, covenants
or agreements herein contained, for which a specific performance is not
provided, which is not cured within thirty (30) days after written notice from
the Landlord, the Landlord may at his election, without notice or demand,
exercise any remedy available at law or in equity including without limitation
any one or more of the following: declare this Lease to be at an end and recover
said Leased Premises and recover such damages as he may have sustained; or he
may without notice or demand and without declaring the Lease ended, reenter and
occupy, remodel or refer the whole or any part of the Premises for the account
of Tenant on such terms and conditions as Landlord deems reasonable, or to
thereafter terminate the Lease even though the Premises have been refer.

     48.  LANDLORD'S DAMAGES. In the event of any default by Tenant, Tenant
agrees to pap to Landlord all amounts necessary to compensate Landlord for all
damage caused by Tenant's failure to perform its obligations under this lease,
including but not limited to the cost of recovering possession of the Premises
(including attorney's fees), the cost of repairs, alterations, leasing
commissions and, all other expenses incurred in maintaining, preserving or
reletting the Premises to a new tenant. Landlord shall be entitled to recover
from Tenant the rent and other charges due and unpaid:, (I) at termination of
the Lease if the Lease is terminated; (ii') if the Lease is not terminated, as
they become due by bringing one or more actions from time to time; or (iii) the
difference between the rental, if any, received by Landlord under any reletting
of the Premises, and the rental to the charges which would have been paid over
the term but for Tenant's default, with present value based on a discount rate
of $%.

     49.  EQUIPMENT, ROOF, WALLS AND OTHER REPAIRS. The Landlord, at his own
expense, shall keep the roof and outside walls of the Leased Premises in good
repair during the term of this Lease.  Landlord agrees to pay for the Common
Area maintenance for the entire subject property. Landlord to maintain HVAC,
Roof, Plumbing, Pipes and Sewer. Air conditioning to be repaired in reasonable
time.

     50   FINANCIAL STATEMENT. If Landlord desires to finance or refinance the
Leased Premises, or any part thereof, Tenant hereby agrees to deliver to any
lender designated by Landlord such financial statements of Tenant as may be
reasonably required by such lender. Such statements shall include the past three
years' financial statements of Tenant. All such financial statements shall be
received by Landlord in confidence and shall be used only for the purposes
herein set forth.

     51.  DISCLAIMERS. The Landlord and Tenant herein agree that there were no
promises, inducements, representations or agreements in connection with this
Agreement except those specifically set forth in writing. In the event of legal
action between any of the signatories to this Agreement to enforce the terms
hereof the prevailing party shall be entitled to reasonable attorneys' fees and
court costs from the party adjudged against.

     52   TIME OF ESSENCE. Time is of the essence of this Lease and every term,
condition, covenant and provision.

     53   BINDING OF HEIRS, ETC. This Lease shall inure to the benefit of and be
binding upon the heirs, executors, administrators, successors and assigns of the
respective parties hereto; except that
<PAGE>

nothing in this paragraph contained shall authorize an assignment of the
interest of Tenant herein without the prior written consent of the Landlord.

     54.  TENANT IMPROVEMENTS. Tenant intends to make improvements to the Leased
Premises after Lease execution. All such improvements shall be performed at
Tenant's sole cost pursuant to plans and specifications approved in writing by
Landlord prior to the commencement of any work. Landlord may grant or withhold
its consent to structural alterations or improvements in Landlord's sole
discretion.

     55.  NOT USED

     56.  AMERICANS WITH DISABILITIES ACT. Tenant shall, at its sole expense,
comply promptly with all applicable statutes, ordinances, rules, regulations,
orders and requirements in effect during the Term or any pact of the Term hereof
regulating the Leased Premises or the use thereof by Tenant. Tenant hereby
covenants that it shall, at its expense, comply promptly with all applicable
provisions of Title III of the Americans' With Disabilities Act, 42 U.S.C. (S)
12181 et se ., and all regulations promulgated thereunder (the "ADA"). Tenant
shall not use or permit the use of the Leased Premises in any manner that will
tend to create waste or a nuisance or which shall tend to disturb occupants of
buildings adjacent to the Premises. Neither Tenant nor its employees, customers
or any person for whom Tenant is responsible shall in any way obstruct or
interfere with the use of any street, sidewalk or passageway in or adjacent to
the Building.

     57.  CONDITION OF LEASED PREMISES. Tenant has had an opportunity to
thoroughly inspect the Leased Premises prior to the date of the signing of this
Lease, therefore, Tenant hereby accepts the Leased Premises "AS IS" in its
condition existing as of the date of the signing of this Lease, without any
representation or warranty, express or implied, oral or written, concerning the
condition, useability, or habitability of the Leased Premises, subject to all
applicable zoning, municipal, county, state and federal laws, ordinances and
regulations governing the regulating the use of the Leased Premises; and Tenant
hereby accepts this Lease subject thereto and all matters disclosed thereby and
by any exhibit; attached hereto, except that (I) heating, cooling and plumbing
systems shall be in operable working condition and (ii) the exterior roof shall
be water tight, as of the date of the signing of this Lease. Tenant acknowledges
that neither Landlord nor Landlord's agent has trade any representation or
warranty as to the suitability of the Leased Premises for the conduct of
Tenant's business. Tenant's singing of this Lease indicates his approval and it
will be presumed that the Leased Premises are satisfactory and the Lease shall
remain in full force and effect as if Tenant had given Landlord notification
that the Leased Premises are suitable for Tenant's business needs.

     58.  HAZARDOUS WASTE. Tenant shall not use, release, produce, dispose,
transport, treat or store in, on, under, or about the Leased Premises any
hazardous waste or toxic substance which is subject to: a) regulation under the
Arizona Hazardous Waste Management Act, A.R.S. 536-2821 et seq.; b) the Resource
Conservation and Recovery Act, 42 U.S.C. 6901 et seq., or c) regulation under
the Toxic Substance Control Act, 15 U.S.C. (S)2601 et seq; or (d) regulation by
any other federal, state, city, county or other statute, governmental
requirement, or authority..

     No activity may occur on the Leased Premises which could have toxic
results. The Leased Premises may be used for the production, treatment,
collection, storage, or disposal of any refuse, objectionable waste or any
material; a) in any manner inconsistent with the regulations issued by the
Arizona Department of Health Services, ACR R9-8-401, et seq.; b) so as to
require a permit or approval from the Arizona Department of Health Services,
pursuant to ACR R9-8-401 et seq., or c) in a manner
<PAGE>

which would cause the County Department of Health Services to inspect the Leased
Premises or issue orders pursuant to Chapter II of the County Health Code.

     Tenant hereby agrees to indemnify, defend, and hold harmless Landlord for
its failure by reason of any breach of this covenant, including any and all
costs, fees; penalties and any other liabilities incurred by Landlord resulting
from such violation of this covenant. In addition to any other rights and
remedies, Landlord may require Tenant to, immediately upon demand, abate any
release of hazardous materials using licensed contractors approved by Landlord,
or Landlord may without notice cause the work to be performed on behalf of
Tenant. Tenant shall pay all costs associated with abatement, remediation or
government enforcement actions arising from Tenant's breach of the foregoing
covenant. Tenant shall give Landlord immediate notice of the release of any
hazardous materials in or about the Premises, and of Tenant's receipt of any
notice or communication from any government authority or other person concerning
compliance of the Premises with any law or regulation relating to health, safety
or the environment ("Environmental Law"), or of the discovery of any condition
which violates or may violate Environmental Law.

     59.  CONDEMNATION. In the event of any condemnation or taking under the
exercise of the power of eminent domain ("Taking") of all or a portion of the
Leased Premises, Landlord shall be entitled to receive the entire award in any
such proceeding, including any award trade for the value of the estate vested by
this Lease in Tenant, and Tenant hereby expressly assigns to Landlord any and
all right, title and interest of Tenant now or hereafter arising in or to any
such award or any part thereof, except for any separate award payable to Tenant
for loss or damage to Tenant's trade fixtures, removable personal property, and
relocation costs. If the entire Leased Premises shall be Taken, then this Lease
shall automatically terminate as of the date Tenant is required by the
condemning agency to vacate the Leased Premises, and all rent and other charges
shall be paid through such date.  If a portion of the Leased Premises shall be
Taken and the use thereof is materially impaired thereby, then either Landlord
or Tenant shall have the right to terminate this Lease as of the date Tenant is
required to vacate such portion of the Leased Premises ("Taking Date") upon
giving the other notice of such election not later than thirty (30) days from
the Taking Date. All rent and other charges shall be paid through the Taking
Date. If the use of the Leased Premises is not materially impaired by the
Taking, or if materially impaired but neither landlord nor Tenant terminates
this Lease, then either such event this Lease shall continue in full force and
effect with respect to the remainder of the Premises except that, as of the
Taking Date, base rent shall be reduced by an amount which is equal to the
proportion thereof that the area taken bears to the entire area of the Leased
Premises before the Taking, and Landlord shall, at its cost and expense, to the
extent practicable restore, the Leased Premises on the land remaining to a
complete unit of like quality and character as existed prior to such Taking.

     60.  NOTICES. All notices or other documents which either party hereto is
required or may desire to give to the other shall be in writing and may be given
by delivering the same personally or by sending the same by certified or
registered mail, postage prepaid, to the addresses which are written below the
signatures of the entities or to such other place as may from time to time be
designated by a written notice. Any notice or other document mailed as aforesaid
shall be deemed sufficiently served or given at the time of mailing thereof.

     61.  LANDLORD'S DEFAULT. Except as otherwise provided in this Lease,
landlord shall be in default under this Lease if landlord fails to perform its
obligations hereunder and said failure continues for thirty (30) days after
written notice from Tenant to Landlord, or if such failure cannot reasonably be
cured within thirty (30) days, if Landlord fails to commence cure within thirty
(30) days and continues diligently to pursue the curing of the same. Landlord's
liability shall in no event exceed the value of Landlord's interest in the
Premises as the same may be encumbered.
<PAGE>

     62.  WARRNTY OF AUTHORITY. The person signing this Lease represents and
warrants that he has authority to do so and that tenant is a duly qualified
corporation.

     63.  FORCE MAJEURE.  Any prevention, delay or stoppage due to strikes,
lockouts, labor disputes, acts of God, inability to obtain labor or materials or
reasonable substitutes therefor, governmental restrictions, governmental
regulations, governmental controls, enemy or hostile governmental action, civil
commotion, fire or other casualty, and other causes beyond the control of the
party obligated to perform shall excuse the performance by such party of a
period equal to any such prevention, delay or stoppage, except the obligations
imposed with regard to rental and other monies to be paid by tenant pursuant to
this Lease.

     IN WITNESS WHEREOF, the said parties to those presents have hereunto set
their hands the day and year first above written.


TENANT:                            LANDLORD:
Chorum Technologies, Inc           Larry Michael Sandusky &
                                   Rebecca Anne Sandusky
By: /s/ Bob Trecartin              By:___________________
   --------------------------
     Authorized Officer            By:___________________
<PAGE>

                      FIRST AMENDMENT TO COMMERCIAL LEASE


THIS FIRST AMENDMEIN"I' TO LEASE (this "Amendment") dated as of July 12th, 2000
is entered into between Larry Michael Sandusky & Rebecca Anne Sandusky
("Landlord") and Chorum Technologies, Inc ("Tenant") and David Nichols Realty,
Inc., ("Agent").

                                   RECITALS

     A.   Landlord and Tenant are parties to that certain Commercial Lease
Agreement dated July 12th, 2000 (the "Lease"), pursuant to which Landlord leased
to Tenant approximately 6,576 square feet of space known as 211 E. 6th Street,
in the County of Pima, City of Tucson, State of Arizona, as more particularly
described in the Lease.

     B.   The parties desire to extend the term of the Lease and to amend and
modify the terms and conditions of the Lease as set forth below.

     NOW, THEREFORE, in consideration of the mutual covenants and promises of
the parties, the receipt and adequacy of which are hereby acknowledged, the
parties hereto agree as follows:

     1.   Leased Premises. Section 1 of the Lease is amended to add at the end
of the section. "The Leased Premises consists of approximately 6,576 square feet
of space."

     2.   Use of the Leased Premise. Section 2 of the Lease is amended to add at
the end of the section "and any other use permitted by law."

     3.   Compliance with Laws. Section 4 of the Lease is amended to add in the
fourth line of the second paragraph after "Premises and the" and before "use
thereof", the following: "Tenant's particular".

     4.   Conduct of Business. Section 5 of the Lease is amended to add at the
end of the section the following: "Notwithstanding the foregoing, Tenant may
vacate the Leased Premises so long as Tenant continues to pay Rent and other
sums due and payable under the Lease and performs all other obligations under
the Terns of the Lease."

     5.   Term. Section 6 of the Lease is amended to extend the term of the
lease through the 8th of October, 2002.

     6.   Rent. Section 7 of the Lease is amended to add at the end of the
section the following:

          for the period from June 3, 2000 up to and including October 8, 2000,
          which Landlord hereby acknowledges receipt. From and after October 9,
          2000, Tenant shall pay to Landlord each month in advance, during the
          term of this Lease, rent in the amount of:

Rental Period                           Monthly Rent

October 9, 2000 - October 8, 2001       $6,576.00
October 9, 2001 - October 8, 2002       $6,850.00
<PAGE>

Rent for partial months of this Lease shall be prorated. The lease remains a
net, net, net lease.

7.   Alterations and Additions. Section 14 of the Lease is amended to add at the
end of the section the following:

Notwithstanding the foregoing, Landlords consent to any request by Tenant for
any alteration, additions or improvements to the Leased Premises shall not be
unreasonably withheld or delayed. Landlord shall, at the time of granting its
consent to any alteration, addition or improvement, shall designate, if
requested by Tenant, whether or not Landlord shall require such alteration,
addition or improvement to be removed at the end of the term as set forth in
this Section 14.

8.   Liens Created by Tenant. Section 15 of the Lease is amended so as to change
the reference in the fifth line of this section from "ten (10) days" to "thirty
(30) days".

9.   Liability Insurance. Section 19 of the Lease is amended so as to change the
reference in the fourteenth line of this section from "rated A+ or better" to
"rated A- or better".

10.  Exemption of Landlord from Liability. Section 20 of the Lease is amended to
add at the end of the second paragraph the following: "Nothing contained herein
shall limit Landlord's obligation to return the Security Deposit". Section 20 is
further amended to add at the end of the section: "Notwithstanding the
foregoing, the exemption from liability contained in this section shall not
apply to the negligence or willful misconduct of Landlord."

11.  Fire or Earthquake. Section 23 of the Lease is amended to replace the
reference to "Thirty (30) working days from the date of such damage," in the
fourth and fifth lines of this section to "Ninety (90) working days from the
date of such damage."

12.  Lease Transfer. Section 27 of the Lease is amended to delete the period at
the end of the last sentence of this section and to add the following: ",
provided Landlord also transfers the Security Deposit to such assignee."

13.  Reasonable Consent. Section 28 of the Lease is amended to delete in their
entirety subsections "a", "d" and "e".

14.  Mortgage. Section 14 of the Lease shall be deleted in its entirety and
replaced with:

Subordination; Sale.

(a)  Subordination. This Lease shall be subject and subordinate at all times to
the lien of all mortgages and deeds of trust securing any amount or amounts
whatsoever which may now exist or hereafter be placed on or against the Leased
Premises or on or against Landlord's interest or estate therein, all without the
necessity of having further instruments executed by Tenant to effect such
subordination. Notwithstanding the foregoing, in the event of a foreclosure of
any mortgage or deed of trust or of any other action or proceeding for the
enforcement thereof, or of any sale thereunder, this Lease; shall not be
terminated or extinguished, nor shall the rights and possession of Tenant
hereunder be disturbed, if Tenant is not in default under the terms of this
Lean, and Tenant shall attorn to the person who acquires Landlord's interest
hereunder through any such mortgage or deed of trust. Tenant agrees to execute,
acknowledge and deliver upon demand such further instruments evidencing such
subordination of this Lease to the Lien of all such mortgages or deed of trust.
Tenant agree; to execute, acknowledge and deliver upon demand such further
instruments evidencing such subordination of this Lease to the lien of all such
mortgages and
<PAGE>

deeds of trust as may reasonably be required by Landlord, but Tenant's covenant
to subordinate this Lease to mortgages or deeds of trust hereafter executed is
conditioned upon each such senior mortgage or deed of trust, or a separate
subordination agreement, containing the commitments specified in the preceding
sentence.

(b)  Sale. If the original Landlord hereunder, or any successor owner of the
Leased Premises, sells or conveys the Leased Premises, all liabilities and
obligations on the part of the original Landlord, or such successor owner, under
this Lease accruing after such sale or conveyance shall terminate and the
original Landlord, or such successor owner, shall automatically be released
therefrom, and thereupon, all such liabilities and obligations of the original
Landlord or such successor owner shall be binding on the new owner, the lease
shall remain in full force and effect, the Tenant shall not be otherwise
disturbed and the Tenant shall attorn to such new owner.

15.  Non-Payment of Rent. Section 47 of the Lease is amended so that the term
"deserted" shall mean Tenant's failure to conduct business in the Premises
thirty (30) consecutive days or more without prior notice to Landlord and
without payment of rent.

16.  Late Charges. If any installment of rent or any sum due from Tenant shall
not be received by Landlord or Landlord's designee within ten (10) days after
the date said rent is due, then Tenant shall pay to Landlord a. late charge
equal to ten percent (10%) of the amount due.

17.  Equipment, Roof, Walls and other Repairs. Section 49 of the Lease is
amended so as to delete the last sentence in this section to be replaced with
the following: "Landlord shall have the HVAC repaired and in proper working
order no later than August 1, 2000. Tenant will assume responsibility for HVAC
once satisfactory repair has been completed.

18.  Tenant Improvements. Section 54 of the Lease is amended to add at the end
of this section the following: "For all other alterations and improvements, the
provisions of Section 14 of the Lease, as amended herein, shah apply."

19.  Americans with Disabilities Act. Section 56 of the Lease is amended to
insert in the fourth line of this section after "Premises or the" and before
"use thereof by Tenant" the following: "Tenant's particular". Section 56 d'
further amended to delete the period at the end of the second sentence and to
add the following: "arising out of Tenant's particular use of the Leased
Premises."

20.  Additional Provisions. The Lease is hereby amended by adding the following
sections:

(a)  64. Parking. The Tenant shall have the right to the exclusive use of twelve
(12) parking spaces in the rear of the building, during the term of this Lease.

(b)  65. Signage. The Landlord reserves the right to place reasonable signage on
6/th/ Street, subject to Tenants prior written consent, which shall not be
unreasonably withheld.

(c)  66. Dumpster Charges. The Dumpster charges for the removal of waste
material will be divided equally between the Landlord and the Tenant during the
term of this Lease.

(d)  67. Additional Brokerage Fee. Any additional brokerage fee as a result of
this Amendment or the exercise of Duly option shall be pursuant to a separate
agreement and shall be paid by Landlord.
<PAGE>

(e)  68. Option to Renew. Landlord grants Tenant one (1) option to renew this
lease for a period of two (2) years, provided Tenant provides Landlord with
written notice not less than sixty (60) days prior to the termination of this
Lease. All of the terms and conditions contained in the Lease, as amended, shall
apply during any option period with the exception of rent which shall be as
follows:

Rental Period                           Monthly Rent
October 9, 2002 - October 8, 2003       $7,124.00
October 9, 2003 - October 8, 2004       $7,398.00

21.  Except as set forth therein, the Lease remains unmodified and in full force
and effect. In the event of any inconsistency between the provisions of the
Lease and this Amendment, the terms of this Amendment shall control.

22.  This Amendment may be executed in two or more counterparts, which when
taken together shall constitute one and the same instrument. The parties also
agree and intend that a signature by facsimile machine shall find the party so
signing with the same effect as though the signature were an original
signature;.

IN WITNESS WHEREOF, Landlord and Tenant have executed and delivered this First
Amendment to Commercial Lease on the date first set forth above.

LANDLORD:                                    TENANT:

Larry Michael Sandusky & Rebecca Anne        Chorum Technologies, Inc.,
Sandusky,

By:  _________________________________       By:    /s/ Bob Trecartin
                                                  ------------------------------

Its: _________________________________       Its: ______________________________


AGENT:

David Nichols Realty, Inc.


By:  _________________________________

Its: _________________________________